eurodns is one of the reputable domain name registrar in the market and domain name cost is depends on the TLD types. You need to visit their official web site and you will find the exact prices of TLD domains along with available discount offers.
As far as cheapest domains are concerned, i would suggest you to go with Godaddy
you will find a lot of coupon codes for Godaddy on different websites/forums to save you even more bucks... i have recently purchased a .info through them & the total amount i have paid for a year was merely $2 (1.90 for domain & 0.10$ for some kinda service charge)
domain name is the most recognized system for assigning addresses to Internet web servers, it gives a website its own unique web address,domain names must be unique on the Internet and registered with the COM, NET, and ORG top-level domains.